The goal of this project is to use in vitro studies in cell lines and primary human cells and human[unreadable] cervicovaginal tissue explants to test candidate siRNA complexes for their ability to target different cell types[unreadable] potentially important in HIV transmission (Langerhans cells and lamina propria T cells, dendritic cells and[unreadable] macrophages), efficiently induce gene silencing and provide protection from challenge with HIV, all without[unreadable] unintended toxicity. siRNAs targeting viral coreceptors and/or HIV genes can prevent viral entry or suppress[unreadable] HIV replication, even in productively infected cells. siRNAs targeting more than one gene have a synergistic[unreadable] effect on blocking HIV replication. A key lesson learned from efforts to develop effective HIV drug regimens[unreadable] is that to control the virus it is necessary to target multiple steps in its lifecycle. One of the advantages of[unreadable] using siRNAs is that it is relatively easy to develop a cocktail of siRNAs that can simultaneously target[unreadable] several genes. HIV can mutate to escape from inhibition by siRNAs, just as it can escape from conventional[unreadable] drugs. One aim of this project is to identify siRNAs that might be included in a cocktail to silence other host[unreadable] genes besides CCR5, as well as conserved HIV target sequences that will provide cross-clade protection[unreadable] and be difficult for the virus to mutate without a loss in fitness. In addition siRNA sequences against[unreadable] macaque CCR5 and the SHIV challenge isolate will be identified for rhesus challenge studies in Project by Veazey.[unreadable] This project will use engineered vaginal tissue and cervicovaginal explants to verify that Langerhans cells[unreadable] and other cells important in HIV transmission are effectively transduced and silenced by siRNA-lipid[unreadable] complexes and protected from HIV transmission. If not, it will work closely with the siRNA Manufacturing and Toxicology Core to design and test[unreadable] modified siRNAs or delivery complexes for enhanced transduction, silencing and protection, using strategies[unreadable] developed by the investigators that have been validated in vivo. As siRNAs are optimized as to sequence,[unreadable] chemical modification for stability and delivery, and formulation, they will initially be tested in primary human[unreadable] cells and tissue models in this project, before testing in mice or macaques in Projects by Palliser and Veazey.